Following return from the Gulf War (GW), veterans have experienced of a constellation of symptoms, designated Gulf War Illness (GWI), that cannot be associated with a single disease. In this regard, GW veterans exhibit structural and functional deficits in the central nervous system (CNS), along with cardiovascular complications. One of the more insidious aspects of GWI is that it is a chronic and progressive disorder; indeed, the number of veterans diagnosed with GWI continues to rise in the post- deployment period. Although the mechanisms underlying the myriad of symptoms associated with GWI remain to be elucidated, some studies have determined that GWI veterans exhibit exaggerated immune responses to physiological stressors, which when combined with other studies support the concept that neuroinflammation is a key component in the etiology and progression of GWI. During the previous funding period we developed a rodent model of GWI in which rats were administered the acetylcholinesterase (AChE) inhibitor pyridostigmine bromide (PB) alone and in combination with repeated restraint stress (RRS). Our ongoing studies have revealed that PB and RRS elicit alterations in cardiovascular, neuroendocrine, neuroimmune and behavioral measures. Perhaps more importantly, our preliminary studies indicate that these PB+RRS-induced alterations are exacerbated by lipopolysaccharide (LPS) or acute exposure to heterogeneous social stressors. Such observations suggest that in addition to baseline differences, a prior history of PB and stress may predispose GWI veterans to exaggerated responses to immune challenges or stressful life experiences after deployment in the GW. Surprisingly, relatively few studies have directly tested this hypothesis to determine the underlying mechanisms responsible for exacerbated responses to stress or immune challenges after exposure to PB. Accordingly, the goal of this project is to directly test our overarching hypothesis that immune challenges and stressful stimuli lead to exacerbated neuroimmune, neurochemical, cardiovascular and behavioral deficits after exposure to cholinesterase inhibition in an animal model of Gulf War Illness. This hypothesis will be tested in the following Aims: ? Aim 1 will examine whether immune or stress challenges lead to potentiated neuroimmune responses in PB+RRS rats ? Aim 2 will determine whether LPS or to exposure social stress enhances cardiovascular complications in enhanced in PB+RRS rats. ? Aim 3 will determined whether the performance of hippocampal and prefrontal cortex-dependent behaviors are adversely affected by LPS administration or acute social stress. Successful completion of these studies will demonstrate that PB treatment in combination with stress elicits fundamental alterations in brain and body responses that may be much more evident following immune and social stress challenges, which would be highly consistent with the progress nature of GWI pathophysiology. Most importantly, these studies will identify loci for therapeutic intervention that can be quickly tested in our model and implemented for the treatment of GWI in our veterans.